This invention relates to a process for the production of hydrocarbon lubricants having high viscosity index (VI) from near linear alpha olefins derived from inexpensive lower alkenes by employing the intermediate production of near linear internal olefin oligomers. More particularly, the invention relates to the discovery that a complex mixture of higher alpha olefins produced by metathesis of slightly branched internal higher olefins can be oligomerized to provide lubricants that possess superior properties relating to pour point and viscosity index.
In the processes known in the art for catalytic conversion of olefins to heavier hydrocarbons by catalytic oligomerization using a medium pore shape selective acid crystalline zeolite, such as ZSM-5 type catalyst, process conditions can be varied to favor the formation of hydrocarbons of varying molecular weight. At moderate temperature and relatively high pressure, the conversion conditions favor C.sub.10 + aliphatic product. Lower olefinic feedstocks containing C.sub.2 -C.sub.8 alkenes may be converted; however, the distillate mode conditions do not convert a major fraction of ethylene. A typical reactive feedstock consists essentially of C.sub.3 -C.sub.6 mono-olefins, with varying amounts of nonreactive paraffins and the like being acceptable components.
U. S. Pat. Nos. 4,520,221, 4,568,786 and 4,658,079 to C. S. H. Chen et al., incorporated herein by reference in their entirety, disclose further advances in zeolite catalyzed olefin oligomerization. These patents disclose processes for the oligomerization of light, or lower, olefins using zeolite catalyst such as ZSM-5. The oligomers so produced are near linear in structure and contain internal olefin unsaturation. These unique olefinic oligomers are produced by surface deactivation of the ZSM-5 type catalyst by pretreatment with a surface-neutralizing base. The processes of Chen et al. provide a particularly useful means to prepare higher olefinic hydrocarbons from inexpensive lower olefins, particularly propylene.
Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have led to the relatively recent market introduction of a number of superior polyalpha-olefin synthetic lubricants, primarily based on the oligomerization of alpha-olefins or 1-alkenes. Well known structure/property relationships have pointed the way to 1-alkenes as a fruitful field of investigation for the synthesis of oligomers with the structure thought to be needed to confer improved lubricant properties thereon. Building on that resource, oligomers of 1-alkenes from C.sub.6 to C.sub.20 have been prepared with commercially useful synthetic lubricants from 1-decene oligomerization yielding a distinctly superior lubricant product via either cationic or coordination catalyzed polymerization. Of notable importance is the inventions described in U.S. Pat. Nos. 4,827,064 and 4,827,073 to M. Wu, incorporated herein by reference, where superior hydrocarbon lubricants are prepared having low methyl to methylene branch ratio by oligomerization of alpha olefins using reduced valence state Group VIB metal oxide catalyst on porous support.
As a feedstock to prepare lubricants by cationic, coordination or Ziegler catalysis the olefinic oligomers provided by the aforementioned Chen process are illsuited for two reasons. First, they comprise predominately internal olefins where alpha olefins are required. Secondly, the olefinic oligomers are slightly branched. The prior art for the preparation of synthetic lubricants teaches the oligomerization of linear alpha olefins to produce lube oligomers where little or no branching is preferred. However, it is known that olefin metathesis carried out between lower alpha olefins such as ethylene and higher internal olefins produces higher alpha olefins. Olefin metathesis is described in Olefin Metathesis by K.J.Ivin, published by Academic Press, wherein Chapter 5 describes olefin metathesis with ethene. The olefin metathesis reaction applied to the olefinic oligomers of Chen et al. could provide a route to alpha olefins suitable for the production of synthetic lubricants.
It is an object of the present invention to provide a process for the production of high VI synthetic lubricants from slightly branched higher internal olefins.
It is another object of the present invention to provide a process for the production of slightly branched and linear alpha olefins suitable for the preparation of lubricant range oligomers.
A further object of the present invention is to provide a process for the oligomerization of slightly and linear alpha olefins using reduced valence state Group VIB metal oxide catalyst on porous support.